1. Field of the Invention
The present invention relates to a diagnostic system for a programmable controller (hereinafter referred to as PC), and more particularity to a diagnostic system enabling the identification of logical addresses where retardations occur during a series of sequential control proceedings.
2. Description of the Related Art
PC's are widely used for controlling a various kinds of controlled objects sequentially with a programmed order.
PC's apply operational commands to actuators such as motors, solenoid valves, etc arranged on various kinds of controlled objects, and output operational commands when PC's sense signals representing the completion of operations output from sensors, such as limit switches for controlling various kinds of controlled objects sequentially with a programmed order.
And if a retardation should occur during a sequential controller proceeding, actions of various kinds of controlled objects are interrupted.
In PC's, however, because many actuators and sensors are connected to PC's, it requires a long time and special knowledge of PC's to determine the cause of a retardation and identify a logical address corresponding to abnormal actuators and sensors.
To simplify an inspection and an identification, PC's with so-called diagnostic function are already suggested (see Japanese Unexamined Patent Application (Kokai) 61-202207).
ON-OFF statuses of contacts arranged on a controlled object are read in this PC synchronizing each sampling time, and logical addresses corresponding to abnormal actuators and sensors are identified by comparing the ON-OFF statuses with a preprogrammed status representing a normal condition.
Therefore, this PC has the following faults.
(1) ON-OFF statuses representing a normal condition must be preprogrammed. PA1 (2) A diagnostic area is limited by capacity of memory which stores an ON-OFF status representing a normal condition and an actual ON-OFF status. PA1 (3) When control logics are modified, modifications for a diagnostic area and diagnostic logic are required.